The present invention is directed to a power supply for a key telephone system.
Present power supplies for key telephone systems must provide a variety of ac and dc voltages. These include a negative 24 volt dc talk and relay voltages which are carefully regulated and filtered, a 10 volt ac lamp voltage, a 20 volt ac buzzer signal and a 110 volt ac ring signal of half the line frequency or 30 Hz. Prior power supply units which would perform the foregoing functions were unduly bulky due in part to ferro-resonant ringing components, had relatively poor voltage regulation and required fusing to prevent short circuiting of many of the supply voltage sections.